A printed circuit board (PCB) is made by first preparing a layout drawing in which electrical conductor patterns for connecting electrical components are set, and then mechanical machining and surface treatment are applied to expose the electrical conductors on an insulation substrate to thereby form a circuit board. A major function of the printed circuit board is to realize electrical connection between the electrical components. Based on the arrangement of the electrical conductor patterns, the printed circuit boards can be classified as singe-sided boards, double-sided boards, and multilayered boards. A printed circuit board that is formed with a flexible substrate is particularly referred to as a flexible printed circuit (FPC), which features light weight, extremely small thickness, softness, flexibility, and freedom of arbitrary shaping.
The double-sided flexible printing circuits find various applications in for example notebook computers, liquid crystal displays, digital cameras, mobile phones, touch panels, and a lot of other consumer electronic products. Taking touch panels as an example, the touch panels are classified as single-layered and dual-layered types according to the wiring lay-out. The single-layered touch panel and the dual-layered touch panel are of almost the same structure, namely comprising a glass substrate and a touch control circuit layer and the glass substrate carrying all wiring patterns thereon. A touch panel must be connected to an external control circuit in order to retrieve an electronic signal corresponding to the coordinates of the point where the touch panel is touched. Conventional means for connection between a touch panel and a control circuit comprises anisotropic conductive rubber or a double-sided flexible printed circuit that is interposed between electrodes of the touch panel and connectors of the control circuit. Recently, to improve the reliability of conduction for the touch panel and the external control circuit, the double-sided flexible printed circuit is gradually replacing the anisotropic conductive rubber.